1. Field of the Invention
The subject invention relates to a cooling assembly for cooling an electronic device such as a microprocessor or a computer chip.
2. Description of the Prior Art
These electronic devices generate a high concentration of heat, typically a power density in the range of 5 to 35 W/cm2. Accordingly, research activities have focused on developing more efficient cooling assemblies capable of efficiently dissipating the heat generated from such electronic devices, while occupying a minimum of space.
A forced air cooling assembly typically includes a heat exchanger and a heat sink, and cools the electronic device by natural or forced convection cooling methods. The electronic device is attached to the heat sink and transfers heat thereto. The heat exchanger typically uses air to directly remove the heat from the heat sink. However, air has a relatively low heat capacity. Such forced air cooling assemblies are suitable for removing heat from relatively low power heat sources with a power density in the range of 5 to 15 W/cm2. However, the increased computing speeds have resulted in a corresponding increase in the power density of the electronic devices in the order of 20 to 35 W/cm2, thus requiring more effective cooling assemblies.
In response to the increased heat produced by the electronic devices, liquid-cooled cooling assemblies, commonly referred to as liquid cooled units (“LCUs”) were developed. The LCUs employ a heat sink in conjunction with a high heat capacity cooling fluid, like water or water-glycol solutions, to remove heat from these types of higher power density heat sources. One type of LCU circulates the cooling fluid through the heat sink to remove the heat absorbed from the heat source affixed thereto. The cooling fluid is then transferred to a remote location where the heat is easily dissipated into a flowing air stream with the use of a liquid-to-air heat exchanger and an air moving device such as a fan or a blower. These types of LCUs are characterized as indirect cooling units since they remove heat form the heat source indirectly by a secondary working fluid. Generally, a single-phase liquid first removes heat from the heat sink and then dissipates it into the air stream flowing through the remotely located liquid-to-air heat exchanger. Such LCUs are satisfactory for a moderate heat flux less than 35 to 45 W/cm2.
The LCUs of the prior art have included an axial inlet for coolant with a diverter to direct the coolant radially outward and into fins or vanes. Examples of such are illustrated in U.S. Pat. No. 4,733,293 to Gabuzda; U.S. Pat. No. 5,597,034 to Barker, III, et al.; U.S. Pat. No. 6,196,300 to Checchetti; U.S. Pat. No. 6,219,242 to Martinez and U.S. Pat. No. 6,719,038 to Bird et al. Each patent discloses a heat sink assembly having radial fins or vanes and used in a LCU. The heat sink assemblies include a base plate with a plurality of fins having smooth sidewalls extending upwardly from the base plate. In operation, the base plate absorbs the heat from the electronic device and transfers the heat to the fins. A cooling fluid flows past the smooth walled fins, drawing the heat from the fins, thereby removing the heat from the heat sink. The flow of cooling fluid is directed parallel to the fins by a central diverter.
The U.S. Pat. No. 5,019,880, issued to Higgins, discloses a heat sink that includes a circular base with a central flow diverter having a conical shape extending upwardly from the base. A plurality of planar fins is disposed radially about the circumference of the flow diverter and extends upwardly from the base to a lid. An inlet is disposed above the lid for directing a flow of cooling fluid axially onto the flow diverter. The flow of cooling fluid then circulates radially outward to the outer periphery of the base through a plurality of flow channels defined between the planar fins.